The present invention relates to hydrocarbon fluids and their uses. Hydrocarbon fluids find widespread use as solvents such as in adhesives, cleaning fluids, solvents for decorative coatings and printing inks, light oils for use in applications such as metalworking and drilling fluids. The hydrocarbon fluids can also be used as extender oils in systems such as silicone sealants and as viscosity depressants in plasticised polyvinyl chloride formulations. Hydrocarbon fluids may also be used as solvents in a wide variety of other applications such as chemical reactions.
The chemical nature and composition of hydrocarbon fluids varies considerably according to the use to which the fluid is to be put. Important properties of hydrocarbon fluids are the distillation range generally determined by ASTM D-86 or the ASTM D-1160 vacuum distillation technique used for heavier materials, flash point, density, Aniline Point as determined by ASTM D-611, aromatic content, viscosity, colour and refractive index. Fluids can be classified as paraffinic such as the Norpar® materials marketed by ExxonMobil Chemical Company, isoparaffinic such as the Isopar® materials marketed by ExxonMobil Chemical Company; dearomatised fluids such as the Exxsol® materials, marketed by ExxonMobil Chemical Company; naphthenic materials such as the Nappar® materials marketed by ExxonMobil Chemical Company; non-dearomatised materials such as the Varsol® materials marketed by ExxonMobil Chemical Company and the aromatic fluids such as the Solvesso® products marketed by ExxonMobil Chemical Company.
Unlike fuels fluids tend to have narrow boiling point ranges as indicated by a narrow range between Initial Boiling Point (IBP) and Final Boiling Point (FBP) according to ASTM D-86. The Initial Boiling Point and the Final Boiling Point will be chosen according to the use to which the fluid is to be put however, the use of the narrow cuts provides the benefit of a precise flash point which is important for safety reasons. The narrow cut also brings important fluid properties such as a better defined viscosity, improved viscosity stability and defined evaporation conditions for systems where drying is important, better defined surface tension, aniline point or solvency power.
These hydrocarbon fluids are derived from the refining of refinery streams in which the fluid having the desired properties is obtained by subjecting the most appropriate feed stream to fractionation and purification. The purification typically consists of hydrodesulphurisation and/or hydrogenation to reduce the sulphur content or, in some instances, eliminate the presence of sulphur and to reduce or eliminate aromatics and unsaturates. Traditionally aliphatic hydrocarbon fluids are produced from the products of atmospheric distillation such as virgin or hydro-skimmed refinery petroleum cuts which are deeply hydrodesulphurised and fractionated. If a dearomatised fluid is required the product that has been deeply hydrodesulphurised and fractionated may be hydrogenated to saturate any aromatics that are present. Hydrogenation can also occur prior to the final fractionation.
There is currently a trend towards the use of fluids with extremely low levels of aromatics, extremely low sulphur levels and with higher initial boiling points. These requirements are driven by environmental and/or safety considerations and/or specific end-uses. The existing processes in which a light gas oil or virgin gas oil obtained from atmospheric distillation is first hydrofined and, if required, hydrogenated are limited to feeds with a maximum ASTM D-86 Final Boiling Point (FBP) of 320° C. Feeds with higher boiling points, which tend to also have higher sulphur levels can render the life of the hydrogenation catalyst too short and the higher content of aromatics in these feeds also limits the material that can be hydrogenated in an economic manner. Generally the boiling range of hydrocarbon fluids is measured using the atmospheric boiling measurement technique ASTM D-86 or its equivalents. However, ASTM D-86 is typically used to measure boiling temperatures up to around 370° C., more typically up to 360° C. If however the fluid contains a fraction boiling above 365° C. it may be more convenient to use the ASTM D-1160 technique which measures the distillation temperature using vacuum techniques. Although the fluids specifically discussed herein are stated to have ASTM D-86 boiling points the boiling range of a fluid having a final boiling point above 365° C. may be measured by ASTM D-1160.
Further requirements for hydrocarbon fluids are that they have good cold flow properties so that their freezing points are as low as possible. There is also a need for improved solvency power particularly when the fluids are used as solvents for printing inks where it is necessary that they readily dissolve the resins used in the ink formulations.
Typically in a refinery the crude oil is first subject to atmospheric distillation to obtain the useful light products. Hydrocarbon fluids which find widespread use as solvents in a wide variety of applications, such as cleaning fluids, ink, metal working, drilling fluids and extenders such as in silicone oils and viscosity depressants for polymer plastisols are obtained from the products of atmospheric distillation. The residue from the atmospheric distillation is then subject to vacuum distillation to take off vacuum gas oil. Vacuum gas oil from the vacuum distillation may then be subjected to cracking to produce upgrade materials. Hydrocracking is a technique that is frequently used to upgrade vacuum gas oil.
Hydrocarbon fluids have high purity requirements; generally sulphur levels below 10 ppm, preferably below 5 wt ppm and frequently less than 1 wt ppm. These very low levels of sulphur are measured by ASTM D-4045. The specifications for hydrocarbon fluids usually require low levels of aromatics. The fluids also need to satisfy tight ASTM D-86 distillation characteristics. These fluids are typically obtained from one of the side streams of atmospheric distillation. However, the sulphur and aromatics content of these side streams, especially from the second or third side streams, tend to be high and these increase as the final boiling point of the stream increases. Accordingly it is necessary to hydrodesulphurise these side streams from atmospheric distillation to remove the sulphur and hydrogenate the streams to remove the aromatics. In practice, this places an upper limit of about 320° C. on the final boiling point of the stream that can be used because the heavy, higher boiling molecules are more difficult to desulphurise and need to be hydrofined at a higher temperature. This in turn leads to an increase in the formation of coke in the reactor. In practice therefore, it is currently not possible with atmospheric streams to get efficiently below 50 ppm of sulphur at final boiling points above 320° C.
Hydrocracking is a technique that is often used in refineries to upgrade vacuum gas oil distilled out of residue from atmospheric distillation or to convert heavy crude oil cuts into lighter and upgraded material such as kerosene, jet fuel, distillate, automotive diesel fuel, lubricating oil base stock or steam cracker feed. In hydrocracking the heavy molecules are cracked on specific catalysts under high hydrogen partial vapour pressure. Typically hydrocracking is performed on material corresponding to crude cut points between 340° C. and 600° C. and boiling in the range 200° C. to 650° C. as measured by ASTM D-1160. Descriptions of hydrocracking processes may be found in Hydrocarbon Processing of November 1996 pages 124 to 128. Examples of hydrocracking and its use may be found in U.S. Pat. No. 4,347,124, PCT Publication WO 99/47626 and U.S. Pat. No. 4,447,315, these documents are not however concerned with hydrocarbon fluids.